fix: SPDX headers (AGPL→PMPL), email, author name

- AGPL-3.0-or-later → PMPL-1.0-or-later in SPDX-License-Identifier lines
- jonathan.jewell@open.ac.uk → j.d.a.jewell@open.ac.uk
- "hyperpolymath" → "Jonathan D.A. Jewell" in author fields

Part of global TODO cleanup (2026-03-16).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

docs/design/eclexia-next-steps.md

@@ -132,6 +132,6 @@ If My-Lang is actually at 75%, the missing stdlib work on Eclexia becomes **even
 
 ---
 
-**Maintainer:** Jonathan D.A. Jewell <jonathan.jewell@open.ac.uk>
+**Maintainer:** Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
 **Date:** 2026-02-07
 **License:** PMPL-1.0-or-later